To help prevent the spread of didymo (rock snot) and other organisms in New Zealand fishing waters anglers must always check, clean and dry their equipment . Didymosphenia geminata (Didymo) in New Zealand urity. Biosecurity New Zealand has since declared the entire South Island an Outbreak Control Area for didymo. This means rivers and lakes remain.

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Not only did the discovery trigger a major biosecurity response here in New Zealand, but it also highlighted didymo as a potential threat to rivers worldwide.

Didymo was known to have a wide distribution in parts of the Northern Hemisphere, with historical reports of blooms in some countries e. However, the New Zealand discovery led to a general belief that we were dealing with an aggressive invasive organism being spread by humans.

Certainly the pattern of spread of didymo in the South Island of New Zealand was consistent with that view. At the same time, ridymo didymo has yet been detected in any North Island rivers, despite ongoing surveillance.

Didymo blooms are unusual because they typically occur in rivers with low nutrient concentrations, i. In New Zealand, this was a particular concern because it seemed that some of our most iconic and pristine rivers were at risk. In suitable conditions, didymo produces thick smothering mats covering large proportions of the river bed. The mats comprising mostly a polysaccharide stalk material can lead to changes in communities of invertebrates and other algae on the river bed.

The blooms look unsightly and are a nuisance.

They affect river users, interfering with angling, sporting and recreational activities, and blocking water intakes. At the time of the NZ discovery only limited information was available on didymo.

Didymo in New Zealand: ten years on | NIWA

Since then there has been considerable research on various aspects of the distribution, ecology, and effects of the species. A significant breakthrough in understanding didymo resulted from of a series of experiments and surveys in New Zealand.


Three findings were pivotal. Firstwe demonstrated phosphorus P -limitation of didymo cell division rates in water from a river with large blooms. In other words, adding P as dissolved reactive phosphorus, DRP caused cell division rates to increase, even though large blooms were already present.

Secondwe showed that the polysaccharide stalks of didymo which form much of the bloom material grew longer when DRP concentrations were low and light was high. Thirdwe showed that low DRP was associated with xealand cell division rates and high didymo cover in rivers across the South Island: All this led to the conclusion that the blooms are caused by low P concentrations.

The mechanism is that when DRP levels are very low, the energy that would have been used to make new cells is xealand into production of carbohydrate stalks — it is the stalks that make up the bulk of the blooms.

This realisation that blooms occurred because of low P solved a puzzle that had, until then, been approached from another angle: Low P as the cause of blooms provides answers to a few questions about distribution. First, taking a New Zealand perspective, why has didymo remained undetected in the North Island?

Quite simply, dissolved P concentrations in North Island rivers are too high. Many North Island rivers have average DRP concentrations greater than 2 ppb, as a result of P-rich catchment geology, more intensive catchment development than in the South Island, or both.

Didymo in New Zealand – Wikipedia

After 10 years, even with efforts to prevent transfer via humans, it is unlikely that no cells have been introduced. Therefore short-term survival might be expected. However, unless concentrations of P decline significantly to levels below 2 ppbblooms will not form in most North Island rivers. Second, taking a global perspective, what caused didymo blooms to suddenly appear in some regions of ibosecurity Northern Hemisphere in the early s? The low P — didymo bloom zealanv supports a plausible hypothesis.

Declines in P concentrations have been documented in some northern rivers, and a range of processes may lead to such declines, from local scale e. There are historical records of didymo presence but as a rare species in many areas which diidymo now experiencing didymo blooms.


If conditions became suitable i. At this stage, to our knowledge, there are still no data that clearly link the appearance of any recent didymo blooms in the Northern Bipsecurity to declines in dissolved P.

We have no doubt that didymo is a recent introduction. There are no historical records of didymo in the South Island, and only one highly likely a case of mistaken identity from the North Island 3. A likely scenario is that didymo arrived in New Zealand following the transformation of didymo in the Northern Hemisphere from a diidymo species with only occasional blooms in some locations to a common species with widespread blooms.

Didymo in New Zealand: ten years on

In an age of increasing tourism and air travel, the transfer of cells to remote locations like the South Island — which also happened to have rivers with perfect conditions for blooms — was almost inevitable.

Jump to Navigation Skip to main content. Didymo in New Zealand: Didymo in the upper Ohau River, Canterbury. Didymo mat, cut open to show the polysaccharide stalks making up the bulk of the mat, with cells at the surface. Relative concentration of dissolved reactive phosphorus DRP, average of monthly data, to is shown by the size of the circles. Sites marked with blue circles have no didymo blooms. Visible didymo has been observed occasionally at sites with red and blue circles.

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